Replies

1. GBA Editor
   Martin Holladay | Sep 19, 2016 12:41pm | #1

   Michael,
   For the time being, I'll leave the lead hazard issue aside -- but you should know that painting over old lead-based paint may not reduce the hazard. There's a lot to say on that issue.

   In most cases, the vapor permeance of interior paint has little effect on wall system performance. That said, an interior vapor retarder (for example, a layer of vapor retarder paint) is required by most building codes in colder climate zones (Zones 5-8 and Marine Zone 4). The effect to which the presence or absence of this layer affects the moisture performance of the wall system is usually exaggerated.

   If you want more specific advice, you should (a) tell us where you live, and (b) describe all the layers of your wall assembly.

   For more information on these issues, see these two articles:

   Vapor Retarders and Vapor Barriers

   Do I Need a Vapor Retarder?

2. 
   user-6323476 | Sep 19, 2016 04:22pm | #2

   Martin,

   Thanks for the reply. I live in Colorado. It's dry as you know, even in winter. The remodel being considered is an older home built in the 50's. I am not a builder so I cannot describe accurately the wall assembly. I am guessing it's fairly standard for Colorado. I am sure it does not have any of the new WRB type materials. The walls already have a layer of latex paint over the old lead paint with the exception of window and door frames.

   To my question, would an interior latex paint with low permeance create any types of water or mold problems vs. a latex paint with a higher permeance rating? Assuming adding a new coat of latex paint could improve existing conditions (reduce potential of water or mold issues), would the choice in paint permeance be different in a warm humid or cold humid climate?

   I'll start a new thread for the lead-based paint treatment question.

   Thanks,

   Michael

3. GBA Editor
   Martin Holladay | Sep 19, 2016 04:29pm | #3

   Michael,
   Q. "Would an interior latex paint with low permeance create any types of water or mold problems vs. a latex paint with a higher permeance rating?"

   A. No.

   Q. "Assuming adding a new coat of latex paint could improve existing conditions (reduce potential of water or mold issues)..."

   A. It cannot.

   Q. "Would the choice in paint permeance be different in a warm humid or cold humid climate?"

   A. No. If you are adding a layer of interior latex paint to a wall that already has at least two layers of paint, the permeance of the paint is fairly irrelevant. Each additional layer of paint reduces the permeance of the paint layer somewhat, but really -- vapor permeance isn't really an issue here.

   If you want to improve the moisture performance of your wall assembly, focus on air sealing -- not on the vapor permeance of the interior paint.

4. Expert Member
   Dana Dorsett | Sep 19, 2016 04:42pm | #4

   The vapor permeance of leaded paint is usually quite low, well under 1-perm. The permeance of any latex you applied over it will barely budge the needle- you might be able measure it under very controlled conditions, but in the real world the relative difference is nil.

   BTW: Having a vapor permeance specified to four significant digits "...2.894 perms..." ) is downright silly, since there is no way the sample to sample variance could be anywhere near that tight, even if painted in a laboratory with robots. In the real world the human-applied samples wouldn't be good to 2 significant digits, but it would probably be within 1.5 digits.

5. 
   user-6323476 | Sep 19, 2016 07:44pm | #5

   Thank you Martin and Dana for your input on this potential project I am considering.